The gait of a legged mobile robot has hitherto been generated by trial and error using a strict dynamic model of the legged mobile robot. As a result, it has been difficult to generate a gait on a real-time basis. For that reason, the applicant proposes, in Japanese Laid-Open Patent Application No. Hei 10 (1998)-86081, conducting gait generation freely by converting a set of standard gaits, designed with the use of an off-line computer, into a set of time-series data including parameters and a body trajectory to be stored in a memory of a microcomputer mounted on a robot, and by calculating a weighted average of instantaneous values of individual gaits whose parameters relating to time such as a walking period are the same.
However, since a gait is calculated through approximation in the proposed technique, the generated gait fails, occasionally, to satisfy the dynamic equilibrium condition. It should be noted here that the “dynamic equilibrium condition” indicates a situation where a ZMP determined from the gravity and inertial force of a desired gait using a strict dynamic model (that expresses behavior of the robot strictly) is equal to a desired ZMP. To be more specifically, it indicates a situation where horizontal component of a moment produced about the desired ZMP by the resultant force of the determined inertial force and gravity of the robot using a strict dynamic model (that expresses behavior of the robot strictly) is zero. (“walking robot and artificial foot” (written by M. Vukobratovic and translated by Kato and Yamashita); published on 1975 by The Nikkan Kogyo Shimbun Kabushiki Kaisha).